Some turbine hot gas path components may include one or more sheets of material applied over a portion or portions of the underlying component. For example, during pre-sintered preform (PSP) fabrication, one or more sheets of material are brazed onto a turbine component, such as a shrouded blade, a nozzle, or a bucket. The sheets are usually overlaid then brazed onto the component to form an external surface or skin. Typically, the sheets are substantially flat or include a curvature that is generally similar to the overall shape of the component surface to which they become attached, although, through pressure, bending, and the like, these flat sheets may be conformed to the underlying component surface during the attachment process.
Certain gas turbine components have shrouds at the outer extremity of the airfoil. The blade shrouds are typically designed with an interlocking feature, usually in the form of a z-notch, which allows each component to be interlocked at its shroud with an adjacent neighbor component when such components are installed about the circumference of a turbine disk. This interlocking feature assists in preventing the airfoils from vibrating, thereby reducing the stresses imparted on the components during operation.
Turbine hot gas path components are typically made of nickel-based superalloys or other high temperature superalloys designed to retain high strength at high temperature, and the shroud material of the turbine component and the interlocking z-notch may not be of a sufficient hardness to withstand the wear stresses and rubbing that occur during start-up and shut down of a turbine engine. To improve the wear at these locations, a hardface chiclet PSP may be brazed or welded to the z-notch to serve as a wear surface. The hardface material bonded to the respective z-notches protects each notch within each shroud from wear arising from frictional contact during operation when the turbine components are under centrifugal, pressure, thermal, and vibratory loading.
Conventional reconditioning after service of a turbine component including a hardface chiclet PSP includes machining off the PSP, hot isostatic pressing (HIP) the turbine component, performing a rejuvenation heat treatment of the turbine component, re-brazing the turbine component with the hardface chiclet PSP or a new PSP, and re-machining the z-notch of the turbine component before returning the turbine component to service.
Machining off the PSP hardface chiclet prevents the reconditioning conditions from causing the hardface chiclet PSP to re-melt and re-flow, but a re-brazing is then required to reattach or replace the PSP prior to returning the turbine component to service. The additional steps of machining prior to the thermal processing steps and re-brazing after these thermal processing steps add time and both labor and material cost to the reconditioning process.